Various techniques for image fusing are known in the patent literature. The Background of the Invention section of U.S. Pat. No. 4,724,303 includes a survey of the patent literature relating to the use of thermal energy for fixing toner images. The disclosure of U.S. Pat. No. 4,724,303 describes an instant-on fuser including a cylindrical, relatively thin metal cylinder supporting a resistive heating foil or printed circuit secured on the inside surface of the cylinder by a high temperature adhesive. The interior of the cylindrical tube contains ambient air. The heating foil or printed circuit is carried on a fiber glass substrate and the heating element is connected to electrical leads extending through caps on the ends of the cylindrical support. The combined thickness of the cylindrical member, the heating circuit and the adhesive is described as being between 0.005 and 0.01 inches.
U.S. Pat. No. 3,948,214 also describes instant start fusing apparatus. Here the fuser roll has a cylindrical member made of quartz or other material which transmits radiant energy from a source located on the interior of the cylindrical member. The cylindrical member has a first layer made of elastomeric material which transmits radiant energy. The first layer is covered with a second layer of material which absorbs radiant energy. A third layer of material covers the second layer of heat absorbing material to effect a good toner release characteristic on the fuser roll surface. The fuser roll layers are relatively thin and have an instant start capability to fuse toner images onto support material, such as paper.
U.S. Pat. No. 3,471,683 describes a heater roll suitable for use as a fuser roller in which heating is produced by a printed circuit formed into the surface of the roll, which receives electrical power through the roller shaft.
U.S. Pat. No. 4,015,027 describes an electrophotographic toner transfer and fusing method wherein a heated image is supported on a roller or belt intermediate transfer medium employed for pressure transfer of dry toner images onto paper. At column 11line 29--column 12, line 38 there appears a detailed discussion of heating of images upon transfer thereof as proposed therein and as taught in the prior art including specifically U.S. Pat. No. 3,591,276 to Byrne.
Reference is made to FIGS. 5a-5c, 6a-6c, 7a and 7b of U.S. Pat. No. 4,015,027. It is seen that in nearly all cases described, the toner is heated to at least its melting point during the transfer stage. In a technique proposed in U.S. Pat. No. 4,015,027 and exemplified by FIG. 6(a), the toner is heated to at least its melting point prior to the transfer zone. In the transfer zone, the toner cools below its melting point during transfer and fusion.
A belt construction characterized in that it has a very low heat capacitance and a thickness of between 15 and about 200 microns is proposed in U.S. Pat. No. 4,015,027. In one embodiment the belt comprises a 50 micron layer of aluminized Kapton having a 25 micron coating of silicon rubber. Another embodiment employs a 12.5 micron layer of stainless steel instead of the Kapton together with a silicon rubber coating. A reflecting layer is incorporated in the belt to reduce heating thereof.
Reference is now made to the following published patent applications and issued patents in the field of electrophotography: GB published Pat. Applications Nos. 2,169,416A and 2,176,904A and U.S. Pat. Nos. 3,990,696, 4,233,381, 4,253,656, 4,256,820, 4,269,504, 4,278,884, 4,286,039, 4,302,093, 4,326,644, 4,326,792, 4,334,762, 4,350,333, 4,355,883, 4,362,297, 4,364,460, 4,364,657, 4,364,661, 4,368,881, 4,378,422, 4,392,742, 4,396,187, 4,400,079, 4,411,976, 4,412,383, 4,413,048, 4,418,903, 4,420,244, 4,435,068, 4,439,035, 4,454,215, 4,460,667, 4,473,865, 4,480,825, 4,501,486, 4,522,484, 4,531,824, 4,538,899, 4,582,774, 4,585,329, 4,586,810, 4,589,761, 4,598,992, 4,603,766, 4,620,699, 4,627,705, 4,678,317. The subject matter in GB Published Patent Applications Nos. 2,169,416A and 2,176,904A, and U.S. Pat. Nos. 4,326,792, 4,411,976, 4,531,824 and 4,538,899 is hereby incorporated by reference.